How to lower alpha in dark areas ?

(Ric) #1

I’m making images of a fire and need to have the lit area show, but turn alpha transparent further from the fire. How can I make the darker ground alpha 0, but get the lightened area near to stay?
I can make the ground image first and calc alpha when image is applied to the floor, but I thought there was a more direct way.

(Duoas) #2

To what are you applying alpha?

If you’re talking about the light cast from the fire, each light has distance and drop-off controls (select your light object and press F5) that allow you to control how far the light shines and how fast it decays.

Does this help?

(Ric) #3

Thanks, but no.
I’ll need to paste the image over a landscape in another application, and I need the landscape to show and have the fire add extra light without a big black square.
I’ll just use a map with caclulated alpha.

(Duoas) #4

Oh, I see.

For best results, you can model an approximation of the target landscape, give it a Lambert pure white (with no specularity) and render, then use that for your alpha.

Good luck.